Film Preservation 101 is an occasional series in which we answer our most frequently asked questions.
You may have heard that old films can be dangerous, and potentially even explosive (we covered this topic in Film Preservation 101: Is Nitrate Film Really Dangerous?) and you’re worried about your grandfather’s home movies that you keep in the basement. The good news is that home movie stock was always made with safety film, which has an acetate cellulose base and isn’t flammable. The bad news is that if you’re keeping those relics of family history in your basement, you may find that when you pull them out, there’s a strong smell of vinegar in the can. What’s going on and what can you do?
What is vinegar syndrome?
Early on, Kodak and other companies that made film stock knew that nitrate film was flammable and potentially dangerous. For a number of (mostly business-related) reasons, the full transition to safety film wasn’t made until the early 1950s. It wasn’t long before archivists and other people who handled film noticed that the acetate base was deteriorating and off-gassing acetic acid, a component of vinegar. Harold Brown, an archivist at the British Film Institute’s National Film Archive, coined the term “vinegar syndrome” to describe not just the smell, but the accompanying catastrophic deterioration that occurs when the film base breaks down. The three main enemies of acetate film are heat, moisture, and acid. Any combination of the three will accelerate a film’s demise.
This film has vinegar syndrome. It not only smells bad, but is highly shrunken, warped, and will not easily transport through any machine needed to view or copy it.
If you encounter films that smell like vinegar, consider it a warning that you need to act. It’s possible that the film is still in really great physical condition. As the film base deteriorates, however, the integrity of the object is compromised and it becomes increasingly difficult to access the images recorded there. What starts with an unpleasant smell will turn into high shrinkage, a separation between the base (the plastic carrier) and the emulsion (the actual images), softening that leads to increased damage, brittleness, and a fused “hockey puck” condition. As a film advances through the stages of vinegar syndrome, it becomes impossible to watch the content on a projector or flatbed viewer without damaging it. Once it has gone too far, even the gentlest of preservation scanners may be unable to make a new copy.
In the Motion Picture Preservation Lab, we monitor the chemical deterioration of acetate films with AD (acid-detecting) strips. Every film we inspect has a strip added to the can as part of the process. We check it a few days later and record the level of acid deterioration based on how far the strip has changed from blue to yellow, or from 0 to 3 (this is similar to any basic pH experiment you may have done in chemistry class but the strips were specially developed for this purpose). A reading of 1.5 is considered the autocatalytic point, at which film can deteriorate at an exponential rate and immediate action is required.
How can vinegar syndrome be prevented?
As with preventing color fading and preserving nitrate, the answer to preventing vinegar syndrome is proper storage. Keeping acetate films cold and dry slows chemical processes and largely prevents vinegar syndrome from taking hold. Even a film with level 2 or 3 vinegar syndrome can be kept in good condition for decades if stored correctly. Slowing down the process of chemical deterioration means that physical deterioration will also slow and buy more time for reformatting if necessary.
How do we fix vinegar syndrome?
This one’s tough, because the answer is we can’t, really. Keeping films cold and dry just buys time. Some institutions have used little packets called molecular sieves to absorb the acetic acid in the enclosed environment of the film can, but the molecular sieves need to replaced periodically, which is costly and labor-intensive. At NARA, we have more than half a million film reels. Proper storage is our best and only solution (and to re-iterate, it works really well!). For smaller institutions or personal collections without access to ideal storage conditions, molecular sieves can be monitored more closely and might help. Just getting those films out of basements and attics and into a main floor closet will go a long way, as well.
When chemical degradation has advanced to physical deterioration (warping, extreme shrinkage, and soft or brittle condition), we need to act quickly to reformat and preserve as much visual information as possible. Some films are so brittle that they cannot be run on even the gentlest of scanners. Some labs will perform a process called “replasticization” which attempts to put some of the moisture and plasticizers back into the film. This is risky because it might not work, and it only gives you one shot on a film scanner. If you set it up wrong, there’s no going back. In those cases, the best solution is sometimes to just keep it frozen and hope that better technology will come in the future.
For more information on vinegar syndrome and how to care for your films, see:
IPI Storage Guide for Acetate Film–published in 1993 but still a comprehensive guide to what vinegar syndrome is and the best way to prevent it
The Home Film Preservation Guide–Chapter 8 covers storage, including how to prepare small film collections for freezing
The Center for Home Movies has solid guidance on caring for home movie collections.
2 thoughts on “Film Preservation 101: Why does this film smell like vinegar?”
There’s a broad assumption that VS can’t be fixed and can only be addressed by optimal storage. I’m not a chemical expert so I can’t argue with that. However, I suspect that a few years ago, everyone (or practically everyone) would have also assumed that nothing could be done to improve faded films, but that wasn’t correct, in view of the service now available in Italy that significantly improves the colour of such prints, albeit without entirely restoring lost colours.
So, I can’t help retaining some otimism that someone will eventually come up with a liquid film treatment application that might halt VS deterioration for (e.g.) 20 years, even if it doesn’t conclusively halt it. From my point of view – as someone with a substantial but not vast personal ‘archive’ – that would be fantastic news as occasional such applications would not be an excessive burden. I have one or two contacts in the field of chemical engineering, so I might seek their opinion on this.
So, my question to anyone with relevant expertise is: am I completely misguided in clinging to such hopes, perhaps because my lack of scientific knowledge means I have not grasped why this is hopeless? Or do you think there’s at least a slim chance that someone could (literally) come up with a solution? It certainly would be a commercial opportunity, in view of the sales that could result.
It’s not a hopeless idea, but it is one that has failed miserably in the past. There are several known chemical applications that promised to preserve films and ended up having disastrous unintended long-term consequences. As a result, we’re more inclined toward the “do less” approach. The closest we have to chemical treatments are with replasticization, which is a last-resort to try to make film pliable enough for duplication. It’s not a permanent solution, and the film will frequently deteriorate more rapidly after treatment.
In general we look to the researchers at places like the Image Permanence Institute, where scientists have been studying the problem since the 1980s. The problem is that film is inherently self-destructive. Both nitrate and acetate bases will break down over time. Heat and humidity increase deterioration; cold temperatures and reduced humidity slow down chemical processes.
I agree that cold storage is more difficult when dealing with personal collections. I would suggest looking at the home storage advice on filmforever.org for guidance on how to care for personal film collections.
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